Control valves which regulate fluid flow within a high pressure system powering one or more fluid guns are of two basic types. A dump valve, when placed between a high pressure fluid pump and the fluid gun, dumps fluid to the atmosphere when the gun is not activated. The pump sees no substantial load when the gun is deactivated, since gun deactivation automatically causes the dump valve to open to atmosphere. In such a system, the pump thus only acts against a high head pressure when the gun is activated and the dump valve is closed to atmosphere. One disadvantage of a dump valve within such a system is that one deactivated gun (and thus one dump valve open to atmosphere) lowers pressure to all guns within the fluid powered system. If any one gun operator for a large cleaning operation thus deactivates his gun, other gun operators powered by the same fluid system are essentially rendered inactive. Since the dump valve is typically placed at the site of each gun, dumping of fluid to atmosphere can also create a nuisance, safety, and clean-up problem for the operator.
Shuttle valves used in such a high pressure system overcome the problems inherent in a dump valve, and accordingly are increasingly used in high pressure systems powering multiple fluid guns. The shuttle valve relieves back pressure on the pump in order to maintain reliable operation of a positive displacement pump, yet prohibits substantial fluid flow to the deactivated gun. When the shuttle valve is opened, all of the available fluid pressure from the pump is thus available to maximize the high pressure capability of the fluid gun. The valve may be automatically activated to prohibit substantial fluid flow to the gun (which occurs when releasing the gun trigger), and a relatively small amount of low pressure fluid then continues to pass to the gun. A desired high pressure above a selected level is thus maintained in the system upstream from the valve. Accordingly, the fluid system is maintained under relatively high fluid pressure levels at all times, so that one gun can be deactivated without affecting the operation of other guns within the same system. A small quantity of fluid is released from the system when the valve is activated to be primarily but not completely closed, and accordingly nuisance, safety, and clean-up problems are also minimized.
The positive displacement pump in a shuttle valve fluid system is thus continually subject to substantially the same back pressure or load, whether one or more of the guns within the system are activated or deactivated. Shuttle valves as described above are preferably adjustable, so that the desired minimum system pressure level can be easily obtained.
One version of a constant pressure valve or shuttle valve as described above is disclosed in U.S. Pat. No. 3,831,845 ('845 Patent). The valve disclosed in this patent maintains a desired high pressure level in a fluid system, so that each of a plurality of fluid guns may be deactivated without affecting the performance of the remaining fluid guns. The release of any one gun trigger thus incompletely closes the constant pressure valve associated with that gun, and fluid passing through the valve is then diverted through a small orifice in the shuttle valve. Since fluid passes through an orifice within the gun when the gun is activated, but at the same time fluid substantially by-passes the shuttle valve orifice, the pressure in the system remains substantially the same or drops only slightly when any one gun is deactivated. According to the '845 Patent, the desired high pressure level is preferably adjustable. Such adjustment may be achieved at the hose end of the valve, although this type of system pressure adjustment is difficult and time consuming for the fluid gun operator. Also, a fairly large wrench is typically required to loosen and re-tighten the components which achieve pressure adjustment.
Improved techniques and apparatus are desired by fluid gun operators so that higher pressure levels and thus more effective cleaning and/or cutting operations are possible. Improved techniques and apparatus are also desired to facilitate easy adjustment of the high pressure level within a system as described above, although the cost of the constant pressure valve should be minimized. The useful life of a constant pressure valve used in conjunction with a fluid gun ideally should be increased, and erosion problems associated with high maintenance and repair costs desirably should be reduced.
The disadvantages of the prior art are overcome by the present invention, and improved techniques are hereinafter disclosed for controlling the pressure level within a high pressure fluid system. The methods and apparatus of the present invention are particularly well suited for obtaining a minimum desired high pressure level in a fluid system including a plurality of fluid guns, with a constant pressure valve associated with each fluid gun. One or more guns in the system may accordingly be deactivated without affecting the performance of the remaining guns. The repair and service costs for the valve of the present invention are reduced, thereby also reducing operator downtime.